Generally, many processors are provided with the function of setting appropriate states for processors and for systems formed from those processors by generating reset interruptions using reset signals and executing system initialization programs.
In a processor provided with the above described structure, when a reset signal is input from the outside as a result of the pressing of a reset button or of the input of power, firstly an activation reset operation is executed so as to initialize the storage element inside the processor. Next, reset interruption is generated inside the processor and a program for initialization processing known as a reset vector is read from ROM (Read Only Memory) connected to the exterior of the processor via a bus. By executing this initialization processing program, the registers used for the settings of each device located in the system or in the processor are set. In this way, the environment is organized so that the various application programs are placed in a state of execution readiness.
It should be noted here that, in order to achieve lower power consumption in the processor, if there is no processing deemed to be indispensable being executed in the processor for a set length of time, the processor is provided with a function of stopping the supply of clocks to the processor. In a processor having this type of function, in order to restart the operation of the processor after the clocks have been stopped, it is normal for a reset signal to be input once again.
However, because the ROM is a low speed memory device, the problem exists that when the processor is reactivated after being placed in a stopped state due to the clock being stopped or the like a considerable length of time is needed until the point when all of the initialization setting processing has ended. In particular, in a system in which the reactivation is performed frequently via stop and reset signals of the processor, the problem exists that the activation wait time of the system, which is due to access to the ROM having to be made at each reactivation, increases.